JP2005244504A - Image reading device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct color balancing when reading an original with high reflectance factor to the components of specific wavelength in an image reading device which does not use an infrared cut-off filter using three-wavelength region luminescent xenon lamp. <P>SOLUTION: In the spectral sensitivity characteristic of a conventional three-line color image sensor, the skirt of the mound of the spectral sensitivity characteristic of an R transparent filter starts from about 570 nm, and a CCD relative spectral sensitivity in the spectrum is 593 nm with the strongest strength of about 40% in R region. On the other hand, in an image sensor having an improved R transparent filter by this embodiment, the skirt of the mound of the spectral sensitivity characteristic starts from about 520 nm, and it turns out that the CCD relative spectral sensitivity in 593 nm spectral is about 80%. In this embodiment, when the original with the high reflectance factor to the components 650 nm or more is read, the influence of the component about 650 nm or more which becomes a problem, can be alleviated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus such as a color image scanner, a color digital copying machine, and the like that exposes a document with a light source and reads reflected light with a color image sensor, and an image forming apparatus including the image reading apparatus. The present invention relates to an image reading apparatus and an image forming apparatus.

2. Description of the Related Art Conventionally, image reading apparatuses used for color digital copiers, etc., use a halogen lamp as a light source and a light source using a three-wavelength light emission type xenon cold cathode discharge tube (hereinafter referred to as a xenon lamp). It is described in Patent Documents 1 and 2. When using halogen lamps, the infrared spectrum contained in the emission spectrum is very large, so an infrared cut filter is essential, and it is difficult to secure the necessary light quantity as the speed of digital color copying machines increases. Therefore, it is difficult to reduce the cost and increase the speed. On the other hand, in the case of using a xenon lamp, since the long wavelength component contained in the emission spectrum is very small, it is possible to eliminate the infrared cut filter that is essential for the halogen lamp, and it is possible to reduce the cost. Also, with respect to the amount of light, since the luminous efficiency is higher than that of a halogen lamp, it is easy to obtain a high amount of light, and the speed of the digital color copying machine can be increased.
JP 9-46533 A JP-A-10-285341

However, when a xenon lamp is used and an infrared cut filter is not used, there is no problem in most color originals, but the influence of a slight long wavelength light may be a problem depending on the original. FIG. 13 shows the spectral spectrum of a typical xenon lamp, and FIG. 14 shows the spectral sensitivity characteristics of a typical CCD color image sensor. FIG. 15 shows the spectral reflection characteristics of the document A as an example in which the influence of the long wavelength light component is not easily generated, and the documents B and C as examples in which the long wavelength light component is easily output. When D65 is used as the light source for the original, the XYZ tristimulus values and chromaticity x, y of each original are as shown in Table 1 below.

Further, when the originals A, B, and C are read with a xenon lamp having the characteristics shown in FIG. 13 and a color image sensor having the characteristics shown in FIG. 14, the output levels are as shown in Table 2 below (values are relative). value).

  Considering the stimulus value X shown in Table 1, the R (red) output of the image sensor needs to be document A <document B <document C, but actually document A <document C <document B. As a result, the document B having a higher reflectivity with respect to a long wavelength component of 650 nm or more has a stronger reddish color, and the relationship with the color value of the document is broken.

Further, in the case of a xenon lamp, the emission spectrum thereof changes abruptly depending on the wavelength, so that some types of originals may have a reading result showing a color different from the original color. FIG. 16 shows the spectral reflectance of document E and document F as examples of documents susceptible to the small peak of 488 nm of the xenon lamp, and document D as an example of documents hardly affected. When D65 is used as the light source for the original, the XYZ tristimulus values and chromaticity x, y of each original are as shown in Table 3 below.

Further, the output levels when the originals D, E, and F are read by the xenon lamp having the characteristics shown in FIG. 13 and the color image sensor having the characteristics shown in FIG. 14 are as shown in Table 4 below.

  Considering the stimulus value Z shown in Table 3, the B (blue) output of the image sensor needs to be document E <document F <document D, but actually document F <document D <document E. As a result, the document E having a higher reflectivity with respect to the 488 nm component has a stronger bluish color, and the relationship with the color value of the document is lost.

  The present invention has been made to solve such problems, and suppresses an increase in cost and a decrease in light quantity as much as possible, reduces the above-described problem of reading results different from the original color, and improves color reproducibility. An object is to provide an excellent image reading apparatus and an image forming apparatus having the same.

The invention according to claim 1 is an image comprising a three-wavelength light-emitting type light source and a color image sensor having R, G, and B transmission filters that read reflected light from a document illuminated by light from the light source. In the reading apparatus, the image reading apparatus further includes a color balance correction filter that corrects the color balance of the reading output of the color image sensor due to the wavelength dependency of the reflectance of the document.
The invention according to claim 2 is the image reading apparatus according to claim 1, wherein the transmission filter also serves as the color balance correction filter.
According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the collapse of the color balance is corrected by setting a spectral transmittance characteristic of the transmission filter. .
According to a fourth aspect of the present invention, there is provided an image comprising a three-wavelength light-emitting type light source and a color image sensor having R, G, and B transmission filters that read reflected light from a document illuminated by light from the light source. In the reading apparatus, the light source has an emission spectrum that corrects the color balance of the read output due to the wavelength dependence of the reflectance of the document.
According to a fifth aspect of the present invention, in the image reading device according to the fourth aspect, the ratio of the spectral component of the R phosphor to the sub-peak component of the spectrum of the G phosphor of the light source within the transmission wavelength range of the R transmission filter is set. The image reading apparatus is characterized by being made smaller.
The invention according to claim 6 is the image reading apparatus according to claim 4, wherein the ratio of the sub-peak component of the spectrum of the G phosphor to the spectrum component of the B phosphor of the light source in the transmission wavelength range of the B transmission filter is set. The image reading apparatus is characterized by being made smaller.
The invention according to claim 7 is an image including a three-wavelength light emitting source and a color image sensor having R, G, and B transmission filters that read reflected light from a document illuminated by the light of the light source. In the reading apparatus, analog / digital conversion means for converting R, G, B image signals of the image sensor into digital image data, and black level is set to zero and white level is set to full scale for each pixel of the digital image data. Means for normalizing and converting to original image data of R, G, B, and means for handling data obtained by subtracting a specified value for each of the R, G, B image data as new image data An image reading apparatus is provided.
According to an eighth aspect of the present invention, there is provided an image comprising a three-wavelength light emitting source and a color image sensor having R, G, and B transmission filters that read reflected light from a document illuminated by light from the light source. In the reading apparatus, analog / digital conversion means for converting R, G, B image signals of the image sensor into digital image data, and black level is set to zero and white level is set to full scale for each pixel of the digital image data. Means for normalizing and converting to original image data of R, G, B, and means for handling data obtained by multiplying a value designated for each of the R, G, B image data as new image data An image reading apparatus is provided.
According to a ninth aspect of the present invention, in the image reading device according to the seventh or eighth aspect, the subtracted value or the multiplied value depends on the level of each of the original image data of R, G, B or a combination of the original image data. An image reading apparatus characterized by having an arbitrary value specified.
A tenth aspect of the present invention is an image forming apparatus including the image reading device according to any one of the first to ninth aspects.

According to the first, second, and third aspects of the invention, the color balance of the read output due to the wavelength dependency of the reflectance of the original can be corrected by the filter.
According to the inventions according to the fourth, fifth and sixth aspects, the color balance of the read output due to the wavelength dependency of the reflectance of the original can be corrected by the light source.
According to the seventh and eighth aspects of the present invention, when the output balance of R, G, and B is lost in a specific document, a fixed value is subtracted from the R, G, and B image data or a coefficient is set. It is possible to correct the balance of R, G, and B that has been lost by multiplication. For this reason, it is possible to improve color reproducibility when reading a document having a high reflectivity for a long wavelength component, a document having a high reflectivity for a component of 488 nm, and the like.
According to the ninth aspect of the present invention, a fixed value for maintaining an output balance of R, G, and B when a document having a high reflectivity for a long wavelength component, a document having a high reflectivity for a component of 488 nm, or the like is read. By setting the table or coefficient table, it is possible to suppress the R, G, B output balance collapse and improve the color reproducibility.
According to the invention of claim 10, in an image forming apparatus such as a color digital copying machine, an improvement in color reproducibility which is an effect of the inventions of claims 1 to 9 can be realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram showing a schematic configuration of an image reading apparatus according to a first embodiment of the present invention. This image reading apparatus includes a light source 1 composed of a xenon lamp, an optical system 3 that focuses light emitted from the light source 1 and reflected by a document 2, and light that is focused by the optical system 3 is converted into an electrical signal to convert the document. A color image sensor 4 that reads the second image, and an image processing block 5 that processes a color image signal generated by the color image sensor 4. The color image sensor 4 is a three-line color image sensor having three CCD linear image sensors 42R, 42G, and 42B each having R, G, and B transmission filters 41R, 41G, and 41B provided in the incident direction.

  FIG. 2 shows the relative spectral sensitivity characteristic of the CCD linear image sensor 42R and the conventional typical three-line color in order to explain the spectral transmittance characteristic of the R transmission filter 41R provided in the CCD linear image sensor 42R in FIG. The spectral sensitivity characteristic of an image sensor and the relative spectral intensity characteristic (spectral spectrum) of a conventional typical xenon lamp are shown. From this figure, in the CCD spectral sensitivity characteristic of a conventional typical three-line color image sensor, the relative spectral sensitivity of a CCD linear image sensor having an R transmission filter is approximately 0% up to about 570 nm. The peak of the short wavelength side of the mountain rises from about 570 nm, and the value in the spectrum of 593 nm having the strongest intensity in the R region is about 40%, whereas the CCD linear having the improved R transmission filter 41R according to the present embodiment In the image sensor 42R, the relative spectral sensitivity is approximately 0% up to about 540 nm, and the bottom of the short wavelength side of the peak of the relative spectral sensitivity rises from about 540 nm, and the value in the spectrum of 593 nm is about 80%. . With such characteristics, it is possible to reduce the influence of components of about 650 nm or more, which is a problem when reading the document B in FIG.

Further, the originals A, B, and C exemplified in the prior art are illuminated with a conventional typical xenon lamp having the characteristics shown in FIG. 2 and read by the color image sensor 4 according to the present embodiment. The output level of B is as shown in Table 5 (values are relative values).

  By comparing this table with Table 2, the ratio of the R output was original A: B: C = 1: 1.25: 1.17. According to this embodiment, the original A: B : C = 1: 1.20: 1.16, and it is understood that the excessive R output in the document B is improved.

  Thus, according to the first embodiment of the present invention, the peak of the spectral transmittance characteristic of the R transmission filter is such that the transmission band of the spectral transmittance characteristic of the R transmission filter of the image sensor substantially includes 550 nm. By widening the skirt on the short wavelength side, it is possible to reduce the phenomenon that the R output increases when a document having a high reflectance with respect to a long wavelength component of 650 nm or more is read, and to improve color reproducibility.

[Second Embodiment]
The basic configuration of the image reading apparatus according to the second embodiment of the present invention is the same as that of the first embodiment (FIG. 1). However, in this embodiment, the configuration of the color image sensor is the same as the conventional one, and the color reproducibility is improved by changing the spectral spectrum of the R phosphor of the xenon lamp.

  FIG. 3 shows spectral characteristics (emission spectra) of R, G, and B phosphors of a typical xenon lamp, and FIG. 4 shows spectral characteristics of the xenon lamp of the present embodiment and spectral characteristics of a conventional xenon lamp. . From FIG. 3, most of the components of about 650 nm or more which are problematic when reading the document B of FIG. 15 are due to the R phosphor, and the light in the R region is not only the R phosphor but also the spectrum of the G phosphor. It can be seen that the sub-peak component is responsible. Therefore, in the xenon lamp of this embodiment shown in FIG. 4, the ratio of the R phosphor is lowered, and the ratio of the component of about 650 nm or more is greatly reduced.

Further, the originals A, B, and C exemplified in the prior art are illuminated by the xenon lamp of the present embodiment having the characteristics shown in FIG. 4 and read by the conventional typical color image sensor. The output levels are as shown in Table 6 (values are relative values).

  By comparing this table with Table 2, the ratio of the R output was original A: B: C = 1: 1.25: 1.17. According to this embodiment, the original A: B : C = 1: 1.23: 1.17 It can be seen that the excessive R output in the document B is improved.

  Thus, according to the second embodiment of the present invention, the ratio of the spectral component of the R phosphor to the sub-peak component of the spectrum of the G phosphor of the xenon lamp within the transmission wavelength region of the R transmission filter of the image sensor is reduced. Therefore, it is possible to reduce the phenomenon that the R output is raised when a document having a high reflectance with respect to a long wavelength component of 650 nm or more is read, and to improve the color reproducibility.

[Third Embodiment]
The basic configuration of the image reading apparatus according to the third embodiment of the present invention is the same as that of the first embodiment (FIG. 1). In this embodiment, the configuration of the color image sensor is the same as that of the first embodiment, and the configuration of the light source is the same as that of the second embodiment.

When the originals A, B, and C exemplified in the prior art are illuminated by the xenon lamp of the present embodiment having the characteristics shown in FIG. 4 and read by the color image sensor of the present embodiment having the characteristics shown in FIG. The output levels of G and B are as shown in Table 7 (values are relative values).

  By comparing this table with Table 2, the ratio of the R output was original A: B: C = 1: 1.25: 1.17. According to this embodiment, the original A: B : C = 1: 1.173: 1.16 It can be seen that the excessive R output in the document B is greatly improved.

  FIG. 5 shows the influence of the long wavelength region in order to compare this embodiment with the prior art, the first embodiment, and the second embodiment. This figure shows a value obtained by multiplying and integrating the spectral sensitivity characteristic of the R transmission filter and the spectral spectrum of the light source from the short wavelength range (350 nm) to the long wavelength range (800 nm) to the wavelength of the horizontal axis. Normalized by a product-sum value of ˜800 nm). In this figure, “CCD R improvement integration” is the first embodiment, “R improvement xenon integration” is the second embodiment, and “CCD + xenon R improvement integration” is the third embodiment.

  From this figure, it can be seen that, for example, in the conventional integration, the product sum value is about 0.81 at 650 nm, and therefore the influence of the wavelength component of 650 nm or more is (1−0.81) = 0.19 (19%). On the other hand, in the first, second, and third embodiments, they are approximately 0.16, 0.17, and 0.13, respectively. Also, from this figure, when compared in the region of about 630 nm to 720 nm, all the embodiments including the present embodiment with the highest value are higher than the conventional example, and the influence of the long wavelength region is reduced. I know that.

  As described above, according to the third embodiment of the present invention, the peak of the spectral transmittance characteristics of the R transmission filter of the image sensor is widened to the short wavelength side, and the xenon lamp within the transmission wavelength range of the R transmission filter is obtained. The ratio of the spectral component of the R phosphor to the sub-peak component of the spectrum of the G phosphor is reduced so that the phenomenon that the R output increases when a document having a high reflectivity for a long wavelength component of 650 nm or more is read is reduced. And color reproducibility can be improved.

[Fourth Embodiment]
The basic configuration of an image reading apparatus according to the fourth embodiment of the present invention is the same as that of the first embodiment (FIG. 1). However, in the first embodiment, the spectral sensitivity characteristic of the R transmission filter is improved, whereas in this embodiment, the spectral sensitivity characteristic of the B transmission filter is improved.

  FIG. 6 shows the relative spectral sensitivity characteristics of a CCD linear image sensor equipped with the B transmission filter and typical conventional ones in order to explain the spectral transmittance characteristics of the B transmission filter provided in the color image sensor of this embodiment. 3 shows a spectral sensitivity characteristic of a three-line color image sensor and a relative spectral intensity characteristic (spectral spectrum) of a conventional typical xenon lamp. As can be seen from the figure, the spectral sensitivity characteristics of the conventional typical three-line color image sensor have a CCD relative spectral sensitivity of about 0% above about 570 nm with a B transmission filter. The long-wavelength side skirt rises from about 570 nm and the value in the spectrum of about 488 nm is about 58%, whereas in the CCD linear image sensor having the improved B transmission filter according to this embodiment, the CCD relative spectral sensitivity is It can be seen that the length of the peak of the CCD relative spectral sensitivity rises from about 550 nm, and the value in the spectrum of about 488 nm is about 45%. Therefore, in this embodiment, the influence of the component of about 488 nm, which becomes a problem when a document having a high reflectance with respect to the component of 488 nm is read, can be reduced.

Further, when the originals D, E, and F exemplified in the prior art are illuminated with a conventional representative xenon lamp having the characteristics shown in FIG. 6 and read by the color image sensor having the improved B filter according to the present embodiment. The output levels of R, G, and B are as shown in Table 8 (values are relative values).

  By comparing this table with Table 4, the ratio of the B output was original E: F: D = 1: 0.92: 0.96, but according to this embodiment, the original E: F : D = 1: 0.95: 0.99, which shows that the excessive B output in the document E is improved.

  Thus, according to the fourth embodiment of the present invention, the long wavelength of the peak of the spectral transmittance characteristic is such that the transmission band of the spectral transmittance characteristic of the B transmission filter of the image sensor does not substantially include 550 nm. By narrowing the skirt on the side to the short wavelength side, the relative spectral sensitivity of about 488 nm is reduced, and the phenomenon that the B output increases when reading a highly reflective original for the 488 nm component is reduced, and color reproduction is achieved. Can improve sex.

[Fifth Embodiment]
The basic configuration of an image reading apparatus according to the fifth embodiment of the present invention is the same as that of the first embodiment (FIG. 1). However, in this embodiment, the configuration of the color image sensor is the same as the conventional one, and the color reproducibility is improved by changing the spectral spectrum of the B phosphor of the xenon lamp.

  FIG. 7 shows the spectral characteristics of the xenon lamp of this embodiment and the spectral characteristics of a conventional xenon lamp. As shown in this figure, by changing the ratio of the B phosphor and the G phosphor and increasing the ratio of the B phosphor, the sub-peak component (488 nm) of the G phosphor of the xenon lamp within the transmission wavelength range of the B transmission filter By reducing the relative spectral intensity and improving the relative spectral intensity of about 445 nm, the 488 nm component / 445 nm component in the conventional light source was 0.0192 / 0.0124≈1.55, whereas in the present embodiment, The light source is greatly improved to 0.0214 / 0.0197≈1.09, and the influence of the component of about 488 nm that becomes a problem when a document having a high reflectance with respect to the component of 488 nm is read can be reduced.

Further, the originals D, E, and F exemplified in the prior art are illuminated by the xenon lamp of the present embodiment having the characteristics shown in FIG. 7 and read by the conventional typical color image sensor. The output levels are as shown in Table 9 (values are relative values).

  By comparing this table with Table 4, the ratio of the B output was original E: F: D = 1: 0.92: 0.96, but according to this embodiment, the original E: F : D = 1: 0.96: 1.04 It can be seen that the excessive B output in the document E is improved.

  Thus, according to the fifth embodiment of the present invention, the ratio of the spectral component of the B phosphor to the sub-peak component of the G phosphor of the xenon lamp within the transmission wavelength region of the B transmission filter of the image sensor is increased. It is possible to reduce the phenomenon that the B output increases when a document having a high reflectance with respect to a component of 488 nm is read, and to improve color reproducibility.

[Sixth Embodiment]
The basic configuration of an image reading apparatus according to the sixth embodiment of the present invention is the same as that of the first embodiment (FIG. 1). In this embodiment, the configuration of the color image sensor is the same as that of the fourth embodiment, and the configuration of the light source is the same as that of the fifth embodiment.

When the originals D, E, and F exemplified in the prior art are illuminated by the xenon lamp of the present embodiment having the characteristics shown in FIG. 7 and read by the color image sensor of the present embodiment having the characteristics shown in FIG. The output levels of G and B are as shown in Table 10 (values are relative values).

  By comparing this table with Table 4, the ratio of the B output was original E: F: D = 1: 0.92: 0.96, but according to this embodiment, the original E: F : D = 1: 0.99: 1.02 It can be seen that the excessive B output in the document E is improved.

  FIG. 8 shows the influence of the sub-peak component (488 nm) of the G phosphor of the xenon lamp in order to compare this embodiment with the prior art, the fourth embodiment, and the fifth embodiment. In this figure, a value obtained by multiplying and integrating the spectral sensitivity characteristic of the B transmission filter and the spectral spectrum of the light source from the long wavelength range (800 nm) to the short wavelength range (350 nm) to the wavelength of the horizontal axis is shown. Normalized by a product-sum value of ˜800 nm). In this figure, “CCD B improvement integration” is the fourth embodiment, “B improvement xenon integration” is the fifth embodiment, and “CCD + xenon B improvement integration” is this embodiment.

  From this figure, it can be seen that, for example, in the conventional integration, since the product sum value is about 0.3 at 480 nm, there is an influence of about 30% around the peak of 488 nm. Further, when compared at 480 nm, it can be seen that all the embodiments including the present embodiment having the lowest value have values lower than the conventional example, and the influence of the peak at 488 nm is reduced.

  Thus, according to the sixth embodiment of the present invention, the long wavelength side skirt of the spectral transmittance characteristic of the B transmission filter of the image sensor is narrowed to the short wavelength side, and the transmission wavelength of the B transmission filter is reduced. Since the ratio of the spectral component of the B phosphor to the sub-peak component of the G phosphor of the xenon lamp in the region is increased, the phenomenon that the B output is increased when a document having a high reflectance with respect to the component of 488 nm is read is reduced. Color reproducibility can be improved.

[Seventh Embodiment]
FIG. 9 is a diagram showing an image sensor and an image processing block of an image reading apparatus according to the seventh embodiment of the present invention. The basic configuration of the light source, the optical system, and the image sensor in this image reading apparatus is the same as that shown in FIG. However, in the present embodiment, the relative spectral intensity characteristics of the light source and the spectral transmittance characteristics of the R, G, and B filters of the image sensor are the same as the conventional representative ones, and the color reproducibility is improved by the image processing block. ing.

  The image reading apparatus of the present embodiment includes an image sensor 14 and an image processing block 15 that processes R, G, and B image signals output from the image sensor 14. The image processing block 15 includes an analog processing unit 16 that performs predetermined analog processing on the R, G, and B image signals output from the image sensor 14, and an AD that converts the output of the analog processing unit 16 into digital image data. For each pixel of the digital image data output from the conversion unit 17 and the AD conversion unit 17, the black level is normalized to zero and the white level is normalized to full scale, and the black, white, and white levels are converted into R, G, and B original image data. A processing unit 18; a fixed value subtraction unit 19 that subtracts a specified value for each of the R, G, and B original image data output from the black level / white level processing unit 18; and a fixed value subtraction unit 19 And a subtraction value setting unit 20 for setting the subtraction value.

  In the image reading apparatus having the above configuration, the R, G, B3 analog image signals output from the image sensor 14 pass through the analog processing unit 16 independent for each system, and are converted by the AD conversion unit 17 for each system. Converted to digital image data. The digital image data of each of R, G, and B is normalized by the black level / white level processing unit 18 so that the black level becomes “zero” and the white level becomes “full scale”. Thereafter, the fixed value subtracting unit 19 subtracts the fixed values of R, G, and B, and passes them to the subsequent stage as image data. The fixed value to be subtracted is set in the subtraction value setting unit 20 by a control unit (not shown). The fixed value can also be set by the user from an operation unit (not shown). For example, a mode such as “red enhancement” or “B enhancement” may be provided so that the mode can be selected.

  As described above, according to the seventh embodiment of the present invention, when the output balance of R, G, and B is lost in a specific document, a fixed value is subtracted by setting from the R, G, and B image data. By doing so, it is possible to correct the balance of R, G, and B that has been broken.

[Eighth Embodiment]
FIG. 10 is a diagram showing an image sensor and an image processing block of an image reading apparatus according to the eighth embodiment of the present invention. Here, the same reference numerals used in FIG. 9 are attached to the same components as those in FIG. 9 (seventh embodiment). In the present embodiment, a coefficient multiplication unit 21 and a coefficient setting unit 22 are provided instead of the fixed value subtraction unit 19 and the subtraction value setting unit 20 in the seventh embodiment.

  In the image reading apparatus having the above configuration, the processing until the R, G, B3 system analog image signals output from the image sensor 14 are output from the black level / white level processing unit 18 is the same as in the seventh embodiment. The same. In the present embodiment, the coefficient multiplication unit 21 output from the black level / white level processing unit 18 multiplies each of the R, G, and B coefficients and passes the result as image data to the subsequent stage. The coefficient setting method in the coefficient setting unit 22 is the same as the subtraction value setting method in the seventh embodiment.

  As described above, according to the eighth embodiment of the present invention, when the output balance of R, G, and B is lost in a specific document, the image data of R, G, and B is multiplied by a coefficient by setting. Thus, the balance of R, G, and B that has been broken can be corrected.

[Ninth Embodiment]
FIG. 11 is a diagram showing an image sensor and an image processing block of an image reading apparatus according to the ninth embodiment of the present invention. Here, the same reference numerals used in FIG. 9 are attached to the same components as those in FIG. 9 (seventh embodiment). In the present embodiment, a calculation unit 23 and a calculation unit setting unit 24 are provided instead of the fixed value subtraction unit 19 and the subtraction value setting unit 20 in the seventh embodiment. As shown in FIG. 11B, the calculation unit 23 includes a fixed value subtraction or coefficient multiplication unit 231, a fixed value or coefficient selection table 232, and a level determination unit 233.

  The R, G, B digital image data output from the black level / white level processing unit 18 is input to the fixed value subtraction or coefficient multiplication unit 231 and also to the level determination unit 233, and R, G, Level determination is performed for each digital image of B, and the result is passed to a fixed value or coefficient selection table 232 as a table address. In the fixed value or coefficient selection table 232, a fixed value or coefficient for each R, G, and B set in advance according to the table address for each input R, G, and B data is passed to the fixed value subtraction or coefficient multiplication unit 231. . The coefficient multiplication unit 231 performs an operation according to the set contents, and passes the result to the subsequent stage as image data. Note that the input data determination level in the level determination unit 233 is set in advance.

  FIG. 12 is an example of a table set in the fixed value or coefficient selection table 232. This table is used for subtraction of fixed values, and the determination level is 4 levels for each of R, G, and B (output table address is 2 bits. R determination level: 16/32/64/128, G determination level: 24/32/64/160, determination level of B: 8/16/32/64), input data is 8 bits each for R, G, and B.

  As described above, according to the ninth embodiment of the present invention, when the output balance of R, G, and B is lost in a specific document, the table is set for the R, G, and B image data. It is possible to correct the balance of R, G, and B that has been lost by performing computation (fixed value subtraction or coefficient multiplication).

  As described above, in each embodiment of the present invention, color reproduction is performed without using an expensive optical filter (infrared cut filter, color conversion filter) that is used to ensure color reproducibility in a conventional image reading apparatus. Can be improved. By applying these image reading apparatuses to the image reading apparatus of a color digital copying machine, the color reproducibility of the color digital copying machine can be improved.

1 is a diagram illustrating a schematic configuration of an image reading apparatus according to a first embodiment of the present invention. It is a figure for demonstrating the characteristic of the R permeation | transmission filter provided in the image sensor in FIG. It is a figure which shows the spectral characteristics of the fluorescent substance of R, G, B of a typical xenon lamp. It is a figure which shows the spectral characteristic of the xenon lamp of the 2nd Embodiment of this invention, and the spectral characteristic of the conventional xenon lamp. It is a figure which shows the influence of the long wavelength area | region in the 3rd Embodiment of this invention, a prior art, 1st Embodiment, and 2nd Embodiment. It is a figure for demonstrating the characteristic of the B transmissive filter provided in the color image sensor of the 4th Embodiment of this invention. It is a figure which shows the spectral characteristic of the xenon lamp of the 5th Embodiment of this invention, and the spectral characteristic of the conventional xenon lamp. It is a figure which shows about the influence of the subpeak component of G fluorescent substance of the xenon lamp in the 6th Embodiment of this invention, a prior art, 4th Embodiment, and 5th Embodiment. It is a figure which shows the image sensor and image processing block of an image reading apparatus by the 7th Embodiment of this invention. It is a figure which shows the image sensor and image processing block of an image reading apparatus by the 8th Embodiment of this invention. It is a figure which shows the image sensor and image processing block of an image reading apparatus by the 9th Embodiment of this invention. It is a figure which shows an example of the table set to the fixed value or coefficient selection table of FIG. It is a figure which shows the spectrum of a typical xenon lamp. It is a figure which shows the spectral sensitivity characteristic of a typical CCD color image sensor. It is a figure which shows the spectral reflection characteristic of the original document which does not produce the influence of a long wavelength light component easily, and the original document which tends to come out. It is a figure which shows the spectral reflectance of the original document which is easy to be influenced by the small peak of 488 nm of a xenon lamp, and an original document which is hard to receive.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Original, 4 ... Image sensor 5, 15 ... Image processing block, 17 ... AD converter, 18 ... Black level / white level processing block, 19 ... Fixed value subtraction unit, 21 ... Coefficient multiplication unit, 23 ... Calculation unit,

Claims (10)

  An image reading apparatus comprising: a three-wavelength light emitting type light source; and a color image sensor having an R, G, B transmission filter that reads reflected light from a document illuminated by light from the light source. An image reading apparatus comprising a color balance correction filter for correcting a color balance collapse of a read output of the color image sensor due to wavelength dependency of a rate.   The image reading apparatus according to claim 1, wherein the transmission filter also serves as the color balance correction filter.   The image reading apparatus according to claim 2, wherein the color balance is corrected based on a spectral transmittance characteristic of the transmission filter.   An image reading apparatus comprising: a three-wavelength light-emitting type light source; and a color image sensor having an R, G, B transmission filter that reads reflected light from a document illuminated by light from the light source. An image reading apparatus having an emission spectrum for correcting a color balance of a read output due to wavelength dependency of reflectance of an original.   5. The image reading apparatus according to claim 4, wherein the ratio of the spectral component of the R phosphor to the sub-peak component of the spectrum of the G phosphor of the light source within the transmission wavelength range of the R transmission filter is reduced.   5. The image reading apparatus according to claim 4, wherein the ratio of the sub-peak component of the spectrum of the G phosphor to the spectrum component of the B phosphor of the light source within the transmission wavelength range of the B transmission filter is reduced.   An image reading apparatus comprising: a three-wavelength light emitting type light source; and a color image sensor having an R, G, B transmission filter that reads reflected light from a document illuminated by light from the light source. Analog / digital conversion means for converting R, G, B image signals into digital image data, and normalizing the black level to zero and the white level to full scale for each pixel of the digital image data, R, G, B Image data, and means for handling data obtained by subtracting a specified value for each of the R, G, and B image data as new image data. Reader.   An image reading apparatus comprising: a three-wavelength light emitting type light source; and a color image sensor having an R, G, B transmission filter that reads reflected light from a document illuminated by light from the light source. Analog / digital conversion means for converting R, G, B image signals into digital image data, and normalizing the black level to zero and the white level to full scale for each pixel of the digital image data, R, G, B And an image processing apparatus comprising: means for converting the original image data; and means for handling data obtained by multiplying the R, G, and B image data by a specified value as new image data. Reader.   9. The image according to claim 7, wherein the value to be subtracted or the value to be multiplied is an arbitrary value designated by a level of each of the original image data of R, G and B or a combination of these original image data. Reader.   An image forming apparatus comprising the image reading apparatus according to claim 1.

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